To purify such gaseous flows one generally proceeds either through a cyclonic filtration, i.e. one causes a turbulence in the flow which projects the suspended particles through centrifugal effect against the walls, or by screening, i.e. passage of the flow through a porous wall retaining the particles.
The filters now in use in this field have to be changed often and rapidly and the new standards require retention yields higher than 90% up to 99.5% and more. These filters are made by removable elements intended to be mounted in adapted frames.